The Linear Zero-Forcing Crosstalk Canceller is Near-optimal in DSL Channels

The design and optimization of orthogonal frequency division multiplex (OFDM) systems typically take the following form: The design objective is usually to maximize the total sum rate which is the sum of individual rates in each frequency tone. The design constraints are usually linear constraints imposed across all tones. This paper explains why dual methods are ideally suited for this class of problems. The main result is the following: Regardless of whether the objective or the constraints are convex, the duality gap for this class of problems is always zero in the limit as the number of frequency tones goes to infinity. As the dual problem typically decouples into many smaller per-tone problems, solving the dual is much more efficient. This gives an efficient method to find the global optimum of non-convex optimization problems for the OFDM system. Multiuser optimal power allocation, optimal frequency planning, and optimal low-complexity crosstalk cancellation for vectored DSL are used to illustrate this point

A near-optimal linear crosstalk precoder for downstream VDSL

This paper presents a linear crosstalk precoder for VDSL that has a low run-time complexity. A lower bound on the data-rate of the precoder is developed and guarantees that the precoder achieves near-optimal performance in 99% of VDSL channels

A Near-Optimal Linear Crosstalk Canceler for VDSL

Crosstalk is the major source of performance degradation in VDSL. Several crosstalk cancelers have been proposed to address this. Unfortunately they suffer from error propagation, high complexity and long latency. In this paper we present a simple, linear zero forcing (ZF) crosstalk canceler. This design has a low complexity, no latency and does not suffer from error propagation. Furthermore, due to the well conditioned structure of the VDSL channel matrix, the ZF design causes negligible noise enhancement. A lower bound on the performance of the linear ZF canceler is derived. This allows performance to be predicted without explicit knowledge of the crosstalk channels, which simplies service provisioning considerably. This bound shows that the linear ZF canceler operates close to the single user bound. So the linear ZF canceler is a low complexity, low latency design with predictable, near-optimal performance. The combination of spectral optimization and crosstalk cancellation is also considered. Spectra optimization in a multi-access channel generally involves a highly complex optimization problem. Since the linear ZF canceler decouples transmission on each line, the spectrum on each modem can be optimized independently, leading to a signicant reduction in complexity.

A Near-Optimal Linear Crosstalk Precoder for VDSL

Crosstalk is the major source of performance degradation in VDSL. In downstream transmission crosstalk precoding can be applied. The transmitted signal is predistorted, such that the predistortion annihilates with the crosstalk introduced in the binder. Several crosstalk precoders have been proposed. Unfortunately they either give poor performance or require non-linear operations, which results in a high complexity. In this paper we present a simple, linear diagonalizing crosstalk precoder with low run-time complexity. A lower bound on the performance of the DP is derived. This allows performance to be predicted without explicit knowledge of the crosstalk channels, which simplies service provisioning considerably. This bound shows that the DP operates close to the single-user bound. So the DP is a low complexity design with predictable, near-optimal performance. The combination of spectra optimization and crosstalk precoding is also considered. Spectra optimization in a broadcast channel generally involves a highly complex optimization problem. Since the DP decouples transmission on each line, the spectrum on each modem can be optimized through a dual decomposition, leading to a significant reduction in complexity

A Near-Optimal Linear Crosstalk Canceler for Upstream VDSL

Crosstalk is the major source of performance degradation in VDSL. Several crosstalk cancelers have been proposed to address this. Unfortunately, they suffer from error propagation, high complexity, and long latency. This paper presents a simple, linear zero-forcing (ZF) crosstalk canceler. This design has a low complexity and no latency and does not suffer from error propagation. Furthermore, due to the well-conditioned structure of the VDSL channel matrix, the ZF design causes negligible noise enhancement. A lower bound on the performance of the linear ZF canceler is derived. This allows performance to be predicted without explicit knowledge of the crosstalk channels, which simplifies service provisioning considerably. This bound shows that the linear ZF canceler operates close to the single-user bound. Therefore, the linear ZF canceler is a low-complexity, low-latency design with predictable near-optimal performance. The combination of spectral optimization and crosstalk cancellation is also considered. Spectra optimization in a multiaccess channel generally involves a complex optimization problem. Since the linear ZF canceler decouples transmission on each line, the spectrum on each modem can be optimized independently, leading to a significant reduction in complexity

Protecting The Robustness Of ADSL And VDSL DMT Modems When Applying DSM

When transmitting data over an ADSL or VDSL link, performance is very important. In order to improve the bit rate that can be achieved over the copper link, a lot of techniques like power backoff (PBO) and dynamic spectrum management (DSM) focus on the crosstalk and try to operate with lower noise margin. Today's ADSL and VDSL modems are very robust. Both in ADSL and VDSL there exist reconfiguration protocols that take care of changing noise environments. The intent of the paper is to know what the impact is of DSM on the robustness of these systems. If the noise increases, the modem may lose showtime, unless the modem can adapt its PSD to compensate for the increase of noise. In this paper, we investigate for DSM the speed and robustness of various online reconfiguration protocols that exist today. We will consider a worst case noise : a noise that also impacts the communication channel that is needed to reconfigure the modem. Since reconfiguration is essential to recover from a degraded environment, the speed and the robustness of this reconfiguration protocol is very important

Waterfilled VDSL Echo Limitation for Rate-Reach Performance Improvement

Digital Subscriber Line (DSL) deployment is evolving to ever higher bit rates resulting in the use of broader spectra. The DSL flavor using the broadest spectrum today is known as VDSL. The reach performance of VDSL is upstream limited as the upstream bands use the highest frequencies. These high frequencies experience more channel attenuation, resulting in smaller SNR values. In this contribution, a way of increasing the upstream reach performance is described. After investigating the VDSL transceiver, the reach performance of a VDSL modem is identified to be dominated by the echo power. Therefore, limiting the downstream echo yields a better upstream receive signal. This results in trading off downstream bit rate for more upstream bit rate. The way to optimally limit the echo isderived and high performance gains can be achieved. Finally, the optimal solution is approximated with a near optimal solution with considerably less complexity. The near-optimal solution performs very well compared to the optimal solution

Waterfilling in MIMO Systems with Power Constraints on Each Transmitter

In this paper we investigate power allocation in MIMO-OFDM systems. We describe the optimal power allocations under two different constraints: a constraint on the total power of all transmitters (TXs) which is applicable in wireless applications, and a constraint on the power of each TX which is more relevant in wireline applications. We describe the optimal TX/RX structure which in combination with the optimal power allocation achieves the MIMO-OFDM channel capacity (under the chosen constraints), with low complexity. Simulations show the benefits of using a total power constraint in place of a per-TX power constraint are largest when the TXs see channels with significantly different attenuations

Power control method for remotely deployed communication service

The present invention relates to a power control method for transceiver units conveying data over discrete tones. The present invention has application inter alia for remotely deployed communication service, and achieves significant gains over existing methods

Method and apparatus for spectrum management for communication channels with crosstalk

The present invention relates to a method for determining at least one operation transmti power over a communication channel coupled to a disturbance causing transceiver, for at least one tone, said communication channel degrading one or more victim communication channels by crosstalk interferences